Membrane fluidity and oxygen diffusion in cholesterol-enriched erythrocyte membrane.

This work studied the effect of cholesteryl hemisuccinate incorporation on membrane fluidity and on the kinetics of oxygen diffusion at different depths in the erythrocyte membrane. Cholesterol concentration in the membrane was expressed as the cholesterol-protein ratio (C/Pt). The membrane fluidity, as assessed by a fluorescence polarization method with diphenyl-hexatriene and 1-(4-trimethylamino)-6-phenylhexa-1,3,5-triene, decreased as the C/Pt ratio increased. Time-resolved fluorescence spectroscopy of pyrene dodecanoic acid (PDA) under an increasing C/Pt ratio in the erythrocyte membrane revealed enhanced oxygen diffusion in the middle of the membrane bilayer (in which PDA was incorporated), which was not the case with pyrene butyric acid (PBA) incorporated in the internal part of the membrane surface. It has generally been accepted that increased membrane fluidity reduces the physical barrier to oxygen permeation. Such conflicting observations on oxygen permeation in the rigidified erythrocyte membrane could be due to variations in oxygen solubility (preferential partitioning) in different polarity microdomains (cholesterol and phospholipid partitions).